We plan to study intracellular mechanisms of oxygen transport and oxygen utlization and to investigate the interrelationships of cellular metabolism and function under conditions of limiting oxygen availability. A central question is: What cellular mechanisms are called into play to maintain the ability of the heat to pump blood when the oxygen supply is diminished? For this purpose we have developed a preparation of isolated adult heart muscle cells which meet stringent criteria of functional integrity. Using this preparation we will examine the role of myoglobin in intracellular oxygen transport in isolated cardiac muscle cells. We will measure simultaneously oxygen consumption, rate of TAP production, intracellular myoglobin oxygenation and redox state of intracellular cytochromes under rigidly controlled steady state conditions of extracellular oxygen supply over a range of 0 - 100 torr. The preparation of isolated heart cells in singularly well adapted to the study of the state of cytochrome oxidase as it functions in situ in the cell. We will quantify the contribution of functional myoglobin to oxygen utilization and establish a correlation between ATP production and oxygen availability in isolated cardiac cells. We will study intracellular oxygen supply in systems of increasing complexity, that is isolated mitochondria, isolated cells, tissue slices and the heart in situ in order to discover the role of control mechanisms at increasing levels of physiological organization.